About Renal Mass

Approximately 80% of kidney masses are found accidentally because abdominal imaging (CT scans, MRIs and ultrasounds) are performed so frequently. Once a mass is found, it is critical to determine if it is benign or malignant and then to determine the best treatment option.

• How do we determine if a mass in the kidney is benign or malignant?

  Some masses are clearly benign, and this can be determined with careful imaging. Simple cysts are fluid-filled sacs in the kidney. If these cysts have no substance other than clear fluid on the inside, they are typically benign and do not require further evaluation. This can be determined with ultrasound, CT or MRI. Some masses contain fat, and these also are typically benign. They are called angiomyolipomas. Any mass that gets brighter after intravenous contrast (“dye”) is administered is more concerning and must be evaluated further for possible cancer.

• What happens next if my mass gets brighter (enhances) after contrast is given in a CT scan?

  Small kidney masses that are found by accident typically grow at a very slow rate and are highly unlikely to metastasize (spread). For this reason, many people with small kidney masses undergo serial imaging to determine if intervention is required. This strategy is called active surveillance. Some people will never require intervention and may have their masses followed indefinitely. Other patients opt to have their masses treated.

• If I decide on treatment, what are the options?
  1. Partial Nephrectomy: This involves removal of just the tumor and is the most common surgical method used for treating kidney masses. Typically, this is performed via a minimally invasive technique called robotic surgery. The mass is removed, and the remainder of the kidney is repaired. This approach has the benefit of preserving kidney function while not sacrificing cancer control should the mass turn out to be a cancer.
  2. Ablation: Ablation is destruction of the mass. Some small masses can be destroyed by inserting a probe into the mass and introducing either extremely cold temperatures (cryoablation) or radio frequency waves. These procedures are guided by CT imaging or ultrasound and require a simple puncture through the skin. Most patients are discharged the same day. In properly selected patients, the cure rate can be close to that of removal of the mass.
  3. Radical Nephrectomy: This is removal of the entire kidney and is generally reserved for larger masses and masses that cannot be removed from the remainder of the kidney while still leaving behind a functioning kidney. Most commonly, this is performed with a minimally invasive technique called robotic surgery, but occasionally tumors are large enough or complex enough that robotic surgery is not feasible.
• Shouldn’t the mass be biopsied before doing surgery?

  Performing a biopsy of a small kidney mass is technically possible but not very common. With some other cancers, such as prostate or bladder cancer, we always perform a biopsy as part of the initial evaluation. With kidney masses, a biopsy is a bit less reliable. Depending upon the size of the mass, there may be as high as a 30% chance of a false negative biopsy in which the biopsy appears to be benign on the biopsy specimen but really is cancer. There is a risk of bleeding with a biopsy as well. Lastly, most enhancing kidney masses are cancer, and the most common benign enhancing kidney mass, oncocytoma, can be difficult to distinguish from a cancer on a biopsy specimen. For these reasons, sometimes a biopsy is not obtained if removal of the mass is planned. When we perform an ablation, we typically attempt to biopsy the mass, since after the ablation it will no longer be possible to determine what the mass was.